Aguilera's birthday isn't until December 18, but last night she celebrated in style, with celebrity guests like Real Housewives stars Bethenny Frankel and Erika Jayne, who performed, in attendance, as well as Jenner, who wore a black and yellow bikini top and matching chaps.

"When XTINA wants u to dress as XTINA for her bday you do it!!!" the Keeping Up With the Kardashians star captioned a Snapchat photo of her posing with the pop star.